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Jay, I have a P0300 code showing up on My 2003 g35 coupe. My

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HI Jay, I have a...
HI Jay, I have a P0300 code showing up on My 2003 g35 coupe. My car most of the time runs fine, but sometimes it hesitates / shakes. For example, my car ran perfectly this morning and this afternoon, it started to hesitate/shake when I started it up and for the second time in 3 days the Check engine light came on. Can you please assist?
Submitted: 2 years ago.Category: Nissan
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10/14/2015
Nissan Mechanic: Jay, Nissan Technician replied 2 years ago
Jay
Jay, Nissan Technician
Category: Nissan
Satisfied Customers: 20,951
Experience: 20+yrs experience with Nissan & Infiniti Trained & Certified.Currently still working for Dealer
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Hi, My name is*****'m happy to help you. During our conversation, I may be presenting you with different things to try, and ask you some Questions to get a better understand of the issue so I can answer your question properly. So stick with me to the end, and I am sure we should be able to get this issue resolved for you!

There is a number of things that can cause a misfire. So I am going to need to pick your brain a bit to get a general idea of your car so I can offer some suggestions or things to check.

First can you tell me how many miles you have on the car and if you have any Mods? If you do have Mods, please list them.

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Customer reply replied 2 years ago
Sure, my car has 167k miles on it. The only mods are a drop in K & N filter and its lowered. Nothing else.
Nissan Mechanic: Jay, Nissan Technician replied 2 years ago

Ok.. Thank you for that information. I am going to start with your K&N air filter. It is a myth on these cars on how they work. This is something I run into all the time. K&N air filters cause a air vortex in the air intake system which would typically be the best way to have air enter the intake system. But not for cars with the MAF sensor right after the air filter air box. The MAF sensors are designed to read air directly. When you cause the vortex the MAF sensor can not meter the air properly and will cause the car to run lean.

I had a customer with a 2007 G35 Sedan with duel intakes and had two K&N air filters and was dealing with a stalling issue. When I tried to explain to him the first step is to remove the air filters and then re-addapt the self learning he looked at me and cursed me out saying I did not know what I was talking about and left the dealer ship. On his way home, he had to prove to me that the filters were not the issue and stopped at a Nissan dealer to pick up a set of air filters. So he took out the K&N's and put the factory filters in. After a week of no stalling he actually called the dealership and asked to speak with me and apologized for his actions and told me what he did and could not believe how simply air filters can cause this.

So like that customer, I will ask you to start with getting a factory air filter. The second thing I am going to ask you. I am sure you changed the spark plugs. What brand spark plugs did you install?

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Customer reply replied 2 years ago
Thanks for the info. I've had the K&N drop in for about the last 125k miles, but I do understand what you are saying so I'll try the paper filter. A far as the spark plugs, I installed NGK Plfr5a-11 this past december (approx 168k miles at the time)
Nissan Mechanic: Jay, Nissan Technician replied 2 years ago

Did you happen to find any oil in any of the spark plug galleys when you did the plugs? Some times oil can seep from the valve cover o-ring into the spark plug galley and cause misfire codes also.

When you change to the paper type air filter, I recommend the dealers filter. The quality is much better, and does not weather as do after market filters. So try that if you would

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Nissan Mechanic: Jay, Nissan Technician replied 2 years ago
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Nissan Mechanic: Jay, Nissan Technician replied 2 years ago

That is a picture I took to show the difference in air filter quality.

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Nissan Mechanic: Jay, Nissan Technician replied 2 years ago

So do you recall seeing any oil in the spark plug tube? Cylinders 5 & 6 are the most common.

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Customer reply replied 2 years ago
Got it. Dealer filter it is. When I changed the plugs, there was no oil in the plug galleys. I had previously had one of the valve covers replaced as the attached/built in spark plug gasket seals were leaking into one of the tubes. That was sometime in 2009. During the last oil change, there was no oil in the plug galleys. I did however have a very difficult time getting the coil pack off of cylinder 1 when I changed the spark plugs. The rubber cap that connects to the spark plug somewhat melted onto the plug so I had to pull out with pliers and buy a new aftermarket coil pack from autozone...
Customer reply replied 2 years ago
oops.. I said during the last oil change in the previous response... please change that to "previous spark plug change"
Nissan Mechanic: Jay, Nissan Technician replied 2 years ago

I have seen after market coils cause issues. But I would start with one thing at a time. The reason why is cause if you do to much, you won't know what fixed it.

I have also see fuel pumps intermittently cause low fuel pressure which can cause misfire codes. I have seen exhaust restrictions cause misfire codes.

So once you go through the air filter, I would then double check all spark plug tubes to make sure they don't have any oil. Then I would inspect the fuel system with a fuel pressure gauge and drive the car and see if fuel pressure drops when it runs ruff. Pressure should be around 56 Psi. Under acceleration around 40 psi

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Nissan Mechanic: Jay, Nissan Technician replied 2 years ago

Do you have any more questions on this?

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Customer reply replied 2 years ago
how do i get a fuel pressure gauge connected to the car? How do view the pressure while I'm diriving the car?
Customer reply replied 2 years ago
Also, regarding the K&N.. its a drop in filter.. not a cone. So there would not be a vortex, correct?
Nissan Mechanic: Jay, Nissan Technician replied 2 years ago

I use a special attachment to tap in by the fuel pressure damper on the fuel rail. I will then run the gauge up by the wipers and lay it there and monitor it while I drive.

I recently had a QX56 that had 56 psi when driving, but under wide open throttle it would drop to 20 psi and start to run poor. I actually took a video if you want to see

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Nissan Mechanic: Jay, Nissan Technician replied 2 years ago
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Customer reply replied 2 years ago
to access the fuel rail, I'd have to remove the upper and lower plenium, correct?
Nissan Mechanic: Jay, Nissan Technician replied 2 years ago

No, just the top engine cover. I would have to take a picture of the fitting I use. It's hard to explain

Remove the two 10 mm bolts, the attachment would then go into the fuel rail after you removed the damper. Then it will mount right on top of the attachment and two long 10 mm bolts are used to tighten everything down.

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Nissan Mechanic: Jay, Nissan Technician replied 2 years ago

Yes, I have a liquid filled gauge if your wondering why it looks wierd

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Nissan Mechanic: Jay, Nissan Technician replied 2 years ago

I need to get off line for the night. Did you have any more questions on this?

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Customer reply replied 2 years ago
Okay. I'll get the fuel system inspected or do it myself if I can get the proper tools together. As far as the intermittent issue with the misfiring, it starting about a month ago and happened a couple of times while I was waiting at a stoplight idle. It seemed to only happen once the ac was on and when the car started to hesitate, I'd turn off the AC and it would go away. Also, I cleaned the MAF with CRC Maf cleaner and everything seemed to be good for about a month. Last week, the issue happened more often. Now, just this past weekend is when I began to be unable to get the car to stop hesitating by just turning off the AC. Now, the issue is happening every other day or so. If I turn off and turn on the car, sometimes it makes the issue go away and I've been able to make it to my destination. Do you see any other issues based on this that may be causing the intermittent misfiring issue?
Nissan Mechanic: Jay, Nissan Technician replied 2 years ago

Since it is happening more frequently, that actually makes it easier to find.

I would start with the air filter. Something as simply as that could play a factor. Plus those K&N filters do take a toll on the MAF sensor. So I would certainly try that and see if there is a change.

The AC turning on and off is a load on the engine. So when the AC is engages, the idle is raised ( but may not seem it ) to accommodate the load. When you turn of off, then of course the idle operation would return back to normal.

If it only happens when stopped and in gear, I would try air filter and check fuel to start. If you had a scanner to monitor fuel trim. That would be the best way to see what is going on. Improper air and fuel trim readings can cause misfire codes as well.

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Customer reply replied 2 years ago
Thanks again for your assistance. Have a good night. I'll let you know if my issues were able to be resolved per your direction.
Nissan Mechanic: Jay, Nissan Technician replied 2 years ago

Your welcome and thank you for using JustAnswer.com

Don't forget to Rate me if your Satisfied with my help. I hope I have provided you with Excellent Service

Thanks Jay!

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Jay
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